1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor (hereinafter referred to as a ‘photoreceptor’) that uses a specified electron transport substance, and an electrophotographic apparatus using the electrophotographic photoreceptor.
2. Description of the Related Art
In recent years, many organic electrophotographic photoreceptors that use an organic photoconductive material have been proposed and put into practical use as electrophotographic photoreceptors, since organic electrophotographic photoreceptors are non-polluting, are low in cost, and since the photoreceptor properties may be variously designed due to the degree of freedom of material selection.
The photosensitive layer of an organic electrophotographic photoreceptor predominantly comprises a layer in which an organic photoconductive material is dispersed in a resin. Many structures have been proposed, for example, a layered-type structure in which a layer in which a charge generation material is dispersed in a resin (charge generation layer) and a layer in which a charge transport material is dispersed in a resin (charge transport layer) are laminated sequentially. Also, a single layer type structure has been proposed, comprising a single layer in which a charge generation material and a charge transport material are dispersed together in a resin.
Of the above, a functionally separated, layered type photoreceptor, in which a charge transport layer is laminated on top of a charge generation layer as the photosensitive layer, has excellent photoreceptor properties and durability, and hence has been widely put into practical use. A hole transport material is generally used as the charge transport material in the charge transport layer of the functionally separated layered type photoreceptor, and hence such a photoreceptor is used in an electrophotographic apparatus that operates with a negative charging process. However, the negative corona discharge used in the negative charging process is unstable compared with a positive corona discharge, and moreover, the amount of ozone generated is large. Hence, there have been problems of adverse effects on the photoreceptor and adverse effects on the usage environment. An organic electrophotographic photoreceptor that can be used with a positive charging process would be effective for resolving such problems.
To make a photoreceptor having excellent durability, as described above, which would be suitable for a positive charging process and have high sensitivity, it is necessary to use a substance having an excellent electron transporting function. Many such substances and photoreceptors using such substances have been proposed. For example, in Japanese Patent Application Laid-open No. 1-206349, Japanese Patent Application Laid-open No. 4-360148, Journal of the Society of Electrophotography of Japan, Vol. 30, p266 to 273(1991), Japanese Patent Application Laid-open No. 3-290666, Japanese Patent Application Laid-open No. 5-92936, Proceedings of the Pan-Pacific Imaging Conference/Japan Hardcopy '98, Jul. 15 to 17, 1998, J A Hall, Tokyo, Japan, p207 to 210, Japanese Patent Application Laid-open No. 9-151157, Papers from Japan Hardcopy '97, Jul. 9 to 11, 1997, J A Hall (Otemachi, Tokyo), p21 to 24, Japanese Patent Application Laid-open No. 5-279582, Japanese Patent Application Laid-open No. 7-179775, Papers from Japan Hardcopy '92, Jul. 6 to 8, 1992, J A Hall (Otemachi, Tokyo), p173 to 176, Japanese Patent Application Laid-open No. 10-73937, Japanese Patent Application Laid-open No. 1-230054, Japanese Patent Application Laid-open No. 8-278643, Japanese Patent Application Laid-open No. 9-190002, Japanese Patent Application Laid-open No. 9-190003, and Japanese Patent Application Laid-open No. 2001-222122, many electron transport substances and electrophotographic photoreceptors using such electron transport substances are proposed and disclosed, and have received attention. Moreover, in the case of a single layer type photosensitive layer, photoreceptors that use a combination of an electron transport substance and a hole transport substance have been disclosed, for example, in Japanese Patent Application Laid-open No. 5-150481, Japanese Patent Application Laid-open No. 6-130688, Japanese Patent Application Laid-open No. 9-281728, Japanese Patent Application Laid-open No. 9-281729, and Japanese Patent Application Laid-open No. 10-239874. have received attention as having high sensitivity, and have been put into practical use in some cases.
Moreover, in the search for photoreceptors having yet better properties, the present inventors have also proposed various photoreceptors that contain a substance having an electron transporting function (disclosed, for example, in Japanese Patent Application Laid-open No. 2000-75520, Japanese Patent Application Laid-open No. 2000-199979, Japanese Patent Application Laid-open No. 2000-143607, and Japanese Patent Application Laid-open No. 2001-142239).
However, with diphenoquinone compounds and stilbenequinone compounds that are already known as substances having an electron transporting function, electrical properties such as residual potential and sensitivity are not sufficiently satisfactory. Hence, there have been aspirations to realize electrophotographic photoreceptors and electrophotographic apparatuses of higher performance by using an electron transport substance having better electrical properties.